There is known a device that opens and closes a door of a vehicle without requiring a user of the vehicle to directly apply the force of the user to the vehicle door. For example, devised is a vehicle door opening/closing device that operates the vehicle door by allowing a sensor unit disposed on the outer surface of the vehicle to detect the movement of the user in a non-contact manner (refer to Patent Literature 1).
Further, devised is an electronic key system (also referred to as a smart system or a key-less entry system) that permits the vehicle door to be locked or unlocked when a mobile device carried by the user is properly verified and a pneumatic pressure change in each tire of the vehicle is determined to be in agreement with a predetermined change pattern (refer to Patent Literature 2).